This invention generally relates to an apparatus for separating either one of two component signals from a composite signal, and, more specifically to an apparatus in a color television system for extracting the color burst signal from the composite color signal.
A conventional discriminating circuit removes an unnecessary DC or AC component by employing passive components, such as capacitors, coils and the like.
FIG. 1 is a conventional discriminating circuit which extracts or eliminates the color burst signal S.sub.B from a composite color signal S.sub.C +S.sub.B in a color television system. The composite color signals S.sub.C +S.sub.B is applied to the base of a transistor 7 through a coupling capacitor 4. The transistor 7 is biased by resistors 8 and 10 and a bypass capacitor 9. When a sampling pulse Ps is synchronized with the color burst signal S.sub.B, it is at the "H" (high) level; at other times, it is at the "L" (low) level, as shown in FIG. 2(b). This sampling pulse Ps is supplied from a sampling pulse input terminal 2 through resistors 5 and 6 to the base of the transistor 7. When the sampling pulse Ps is at the "H" level, the transistor 7 is in the "ON" state; however, when the sampling pulse Ps is at the "L" level, the transistor 7 is in the "OFF" state. Thus, the conduction of transistor 7 is controlled in accordance with the sampling pulse. When the transistor 7 is in the "ON" state, the collector current I.sub.1 of the transistor 7 is a multiple signal consisting of the burst signal S.sub.B and the sampling pulse Ps, as shown in FIG. 2(c). Because the collector current I.sub.1 includes the unnecessary sampling pulse Ps, the sampling pulse Ps must be eliminated from the collector current I.sub.1. A capacitor 11 and the primary coil 12a of a transformer 12 form a parallel resonant circuit. One side of this resonant circuit is connected to the collector of the transistor 7, and the other side is connected to a voltage source Vcc through a resistor 13. A bypass capacitor 14 is connected to the other side of the resonant circuit in parallel with the resistor 13. Therefore, the collector current I.sub.1 is supplied from the voltage source Vcc to the resonant circuit through the resistor 13. The resonant frequency of the resonant circuit is tuned to that of the burst signal S.sub.B. Accordingly, the color burst signal S.sub.B appears at the output terminals 3 of the secondary coil 12b. Because the frequency of the sampling pulse Ps is different from the frequency of the burst signal S.sub.B, the sampling pulse Ps is not included in the output of the secondary coil 12b. Only the burst signal S.sub. B, not including the sampling pulse Ps, is fed to the output terminals 3 of the secondary coil 12b, as shown in FIG. 2(d). Since the conventional discriminating circuit removes the sampling pulse Ps through the use of passive components like the capacitor 11 and the coil 12, it is difficult to make the circuit in the form of an integrated circuit.